History of the Peloponnesian War

The news of the revolt of the cities quickly reached the Athenians also; and when they learned that troops under Aristeus were also on the way to support the rebels, they sent against the places in revolt two thousand of their own hoplites and forty ships, under Callias son of Calliades with four other generals.

These first came to Macedonia and found that the former thousand had just taken Therme and were besieging Pydna;

so they also took part in the siege of Pydna. But afterwards they concluded an agreement and an alliance with Perdiccas, being forced thereto by the situation of Potidaea and tie arrival of Aristeus, which compelled them to hasten, and then they withdrew from Macedonia.